Huperzine A, which is a Lycopodium alkaloid, has been isolated from the plant Huperzia serrata. It has been shown to inhibit the cholinesterase enzyme and, therefore, has been tested for the treatment of diseases of the cholinergic system. For example, Huperzine A is being studied for the treatment of myasthenia gravis, Alzheimer's dementia and for the improvement of senile memory loss. See J. Liu, et al., The Structures of Huperzine A and B Two New Alkaloids Exhibiting Marked Anticholinesterase Activity, Can. J. Chem., 64, 837-839 (1986).